Closure system

ABSTRACT

A foil of a tagger ring foil (TRF) closure system for a container, such as a can, is provided. The foil comprises a composite of two or more layers made from different materials instead of aluminum only.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/164,446 filed May 25, 2016, which is a continuation of U.S.application Ser. No. 14/459,957 filed Aug. 14, 2014, which was acontinuation of U.S. application Ser. No. 13/829,120 filed Mar. 14,2013, which was a continuation of U.S. application Ser. No. 13/561,585filed Jul. 30, 2012, which was a continuation of U.S. application Ser.No. 13/316,955 filed Dec. 12, 2011, which was a continuation of U.S.application Ser. No. 13/092,257 filed Apr. 22, 2011, which was acontinuation of U.S. application Ser. No. 12/806,782 filed Aug. 19,2010, which was a continuation of U.S. application Ser. No. 12/593,737filed Sep. 29, 2009, which was a national stage filing under 35 U.S.C.371 of PCT/AU2008/000441 filed Mar. 28, 2008, which InternationalApplication was published by the International Bureau in English on Oct.9, 2008, and which International Application claims priority toAustralian Application No. 2007901666, filed Mar. 30, 2007, each ofwhich are hereby incorporated herein in their entirety by reference.

FIELD OF THE INVENTION

The present invention relates to containers having a closure system thatprovides a high barrier to moisture or oxygen.

The present invention relates particularly, although by no meansexclusively, to containers made from metal.

DESCRIPTION OF RELATED ART

Certain dry products are highly sensitive to moisture in that theproducts degrade due to absorption of moisture. For example, milkpowders and infant formulations contain labile vitamins which maydegrade rapidly if excessive moisture levels are reached. As a furtherand more extreme example, certain types of nutritional/flavoured milkadditives have been found by the applicant to be extremely moisturesensitive, requiring less than a 2% increase in weight due to moisturepickup to become unusable.

Other products are very sensitive to oxygen in that the products degradedue on exposure to oxygen. Products in this category include, forexample, instant coffee, infant formula, milk powder, drinkconcentrates. Many of these products are also sensitive to moisture.

In order to avoid moisture and/or oxygen contact, products of the typesdescribed above have traditionally been and are still packed inhermetically sealed metal cans. For ease of access, high performancere-sealing, and tamper evidence, the metal cans typically comprise aclosure system referred to in the art as a “tagger ring and foil” (TRF)closure system.

A traditional TRF system comprises a first component in the form of a“ring”, a second component in the form of a “lever plug”, and a thirdcomponent in the form of a foil sheet.

The ring of the traditional TRF system is adapted to be sealed to a canbody by a process of double seaming as understood in the art of canmanufacture and comprises a flowed-in sealant also according to theknown art. The sealant is typically a rubber composition that providesdesirable sealing properties under compression. The ring furthercomprises a central orifice. The orifice is defined by an annular wallhaving an edge that extends into the container.

The lever plug of the traditional TRF system comprises a flat panel thatis formed to close the orifice with an interference fit. The lever plugfurther comprises a flange that extends outwardly from the panel abovethe vertical wall of the orifice when the plug is positioned in theorifice. The flange prevents the plug being pushed inside the can andmakes it possible to lever the plug out of the can with an appropriateimplement such as a spoon to thereby gain access to the contents of thecan.

For the purposes of this specification a seal resulting from aninterference fit is understood to be a seal provided by forcing onecomponent of controlled diameter, in this case a lever plug, into anorifice of controlled diameter in another component, in this case aring, where the diameter of the one component, i.e. the lever plug, isgreater than or equal to the diameter of the other component, i.e. theorifice in the ring.

The foil of the traditional TRF system is located inside the can andextends from a seaming flange on the ring across the entire end of thecan. The foil is restrained in the seaming flange and is encapsulated inthe double seam at sealing. The foil may be restrained by applyingsealing material over an edge of the foil.

In use, the foil provides an hermetic seal for the contents of a can upto the time that a consumer opens the can and ruptures the foil.Thereafter, the interference fit between the ring and the lever plugmakes it possible to re-seal the can with sufficient moisture barrier tomaintain product quality during successive cycles of removing the leverplug and removing contents from the can and then inserting the leverplug back into the can and re-sealing the can.

For reasons of strength, aluminium foil has traditionally been used asthe foil in traditional TRP closure systems. However, aluminium foil isexpensive. In addition, aluminium foil can form sharp edges when thefoil is ruptured to enable access to a can and the sharp edges can cutconsumers as the consumers remove the contents of the can from the can.The applicant has found that this is a particularly serious issue fromthe viewpoint of marketability of the cans. Further, in times ofincreasing environmental consciousness, the use of aluminium foil as aseal in a metal can, such as a steel can, is undesirable as thealuminium is a contaminant when re-cycling the metal can.

For the above reasons, there is a need for an alternative to thetraditional TRF closure system that does not include the use of analuminium foil at all or at least reduces the amount of aluminium in theTRF system compared to the amount of aluminium in the traditional TRFclosure system and that can be used in a conventional manufacturingprocess for cans or other containers.

In particular, there is a need for an alternative to the traditional TRFclosure system that addresses the issue of sharp edges that form whenthe aluminium foil of the traditional TRF closure system is ruptured.

The above description is not to be taken to be an indication of thecommon general knowledge in Australia or elsewhere.

SUMMARY OF THE INVENTION

According to the present invention there is provided a foil of a taggerring foil (TRF) closure system for a container, such as a can, thatcomprises a composite of two or more layers made from differentmaterials instead of aluminium only.

Preferably the materials that form the layers of the composite foil andthe combination of the layers are selected so that, in use, when thefoil is part of a TRF closure system on a container and the foil isruptured to gain access to the contents of the container, the rupturedfoil does not form with a sharp edge that can cut consumers.

Preferably the materials that form the layers of the composite foil andthe combination of the layers are selected so that the foil can beprocessed in a conventional container manufacturing process thatincludes forming the container with a TRF closure system.

Preferably the composite foil has a board burst strength, when measuredwith Australian Standard (AS) 1301.438s, of less than 400 KPa.

Preferably the composite foil has a cross direction ring crushresistance pressure, defined as the ring crush measured using AS1301.407s, divided by 0.152 and multiplied by the foil thicknessmeasured using AS 1301.426s, of less than 10 MPa.

The applicant has found that the parameters of the board burst strengthand the ring crush resistance pressure of a foil provides an indicationof the “hardness” of the foil and hence the likelihood of a rupturedfoil presenting a sharp edge that could cut a consumer.

In addition, the applicant has found that the composite foil makes itpossible to reduce if not replace altogether the aluminium of thealuminium foil of the traditional TRF closure system while retainingmoisture and oxygen performance and being able to process the foil in aconventional container manufacturing process that includes forming thecontainer with a TRF closure system.

Preferably the composite foil comprises a composite of the followinglayers: paper layer, a first polymer layer, a metal (including a metalalloy) layer, and a second polymer layer. With this arrangement, themain functions of the paper layer are: (a) bulk at low cost, (b) hightensile strength to permit seaming without fracture, (c) easy tearingfor consumer access to the contents of a container, and (d) minimiserisk of a consumer being cut by exposed edges of a ruptured compositefoil. The main function of the first polymer is to adhere together thepaper layer and the metal foil layer. The main function of each of themetal layer and the second polymer layer is to provide moisture andoxygen barrier properties.

Preferably the paper ranges in thickness between 25 and 100 gsm.

Preferably the first polymer layer ranges in thickness of between 10 and30 um.

Preferably the polymer of the first polymer layer comprises aco-extrusion of a low density polyethylene co-extruded and an acrylicacid resin such as ethylene acrylic acid resin.

Preferably the metal of the metal layer of the composite foil comprisesaluminium.

Preferably the metal layer has a thickness of between 7 and 60 um.

More preferably the metal layer has a thickness of less than 40 um.

More preferably the metal layer has a thickness of between 20 um and 40um.

Preferably one of the layers comprises a filler added for the purpose ofreducing the board burst or ring crush resistance pressure to a requiredlevel.

The composite foil may comprise any combination of materials needed toachieve a required moisture and oxygen barrier, board burst strength andring crush resistance pressure.

Preferably the composite foil is applied to a can so the paper side ofthe foil is an outward facing side of the foil.

According to the present invention there is also provided a tagger ringfoil (TRF) closure system for a container, such as a can, that comprisesthe above-described composite foil.

According to the present invention there is also provided a container,such as a can, that comprises the above tagger ring foil (TRF) closuresystem.

Preferably the composite foil of the closure system is applied to thecontainer so that the paper side of the foil is an outward facing sideof the foil.

Preferably the container is a metal container.

Results of Foil Testing

The importance of an appropriate board burst strength and ring crushresistance pressure is illustrated in the following examples that relateto test work on a group of samples.

In the examples:

-   -   The thickness of samples was measured using AS 1301.426s.    -   The board burst strength of samples was measured using the board        burst test according to AS 1301.438s.    -   The ring crush resistance pressure of samples was measured using        AS 1301.407s.    -   The ring crush resistance pressure of a composite foil sample in        accordance with the present invention was measured in a cross        direction of the paper layer of the foil sample. The foil sample        comprised the following layers: paper, a first polymer,        aluminium foil, and a second polymer    -   The cutting ability of the samples was assessed on the basis of        an assumption that this is related to the ring crush resistance        pressure divided by the cross sectional area of a sample being        crushed. The length of a ring crush sample was 152 mm. Prom the        measured ring crush resistance pressure and the thickness of the        sample a parameter, hereafter referred to as ‘ring crush        resistance pressure’, was determined by dividing the measured        ring crush resistance pressure value by 152 mm and the measured        thickness.    -   The ability of the samples to cut fingers was determined        subjectively using a ‘fingertip hardness’ test by a laboratory        technician determining how hard a sample feels against his/her        fingertips.

The applicant tested the board burst strength and ring crush resistancepressure of the samples on the basis that these parameters are goodindicators of fingertip hardness of the samples, with harder samplesbeing more likely to cut consumers.

Burst was chosen as a test as the board burst test, which involves ahydraulic piston driving a rubber diaphragm about 25 mm in diameterthrough a sheet of material, is thought to replicate a consumer seekingto burst through a sheet of unbroken foil of a TRF closure system on acan to gain access to the contents of the can.

A series of aluminium and composite foil samples were measured andtested as described above. The cutting ability of the different sampleswas subjectively assessed. The samples received were aluminium foilsamples of nominal thicknesses of 100 um, 90 um, 60 um, 30 um and 15 um.The performance of this traditional foil material was compared to thatof one embodiment of a composite foil in accordance with the presentinvention, as described above. The composite foil had a nominalthickness of 120 um.

The results of the tests are shown in Table 1 below.

TABLE 1 Results of testing aluminium and composite foil samples. Ringcrush Measured Board burst, resistance Fingertip Sample thickness, umKPa Ring crush, N pressure, MPa hardness ‘100 um’ 106 1087 388 24.1 Highaluminium foil ‘90 um’ 101 929 308 20.0 High aluminium foil ‘60 um’ 67735 158 15.5 Medium aluminium foil ‘45 um’ 50 470 87 11.5 Mediumaluminium foil ‘30 um’ 31 — 39 8.3 Soft aluminium foil ‘15 um’ 16 — (*)6 2.6 Soft aluminium foil Composite foil 122 343 115 6.2 Soft

-   -   Although the board burst strength for the 15 um sample was not        measured, the sample was measured with the similar paper burst        test, AS 1301.403s. A value of 77 kPa was measured. Overall, the        board burst and paper burst strengths were broadly comparable,        for example the composite foil sample had a paper burst strength        of 312 kPa and a board burst strength of 343 kPa.        Table 1 shows that:    -   The board burst strength and the ring crush resistance pressure        of the traditional aluminium foil samples reduced significantly        with a reduction in thickness. However, whilst these results        suggests that reducing the thickness of aluminium foil used in        traditional TRF closure systems is one option for minimising the        current cutting problem, this is not an option form the        viewpoint of manufacturing on current can manufacturing lines.    -   The fingertip hardness of the traditional aluminium foil also        changes as the thickness of the aluminium changes, moving from        hard to soft.    -   As indicated above, the properties of board burst strength and        ring crush resistance pressure are good indicators of fingertip        hardness. The results indicate that values of 400 kPa and 10        MPa, respectively, for board burst strength and ring crush        resistance pressure are approximate dividing lines between soft        and hard samples.

DESCRIPTION OF THE DRAWINGS

The present invention is described further by way of example withreference to the accompanying drawings, of which:

FIG. 1 is a transverse section of a traditional TRF closure system;

FIG. 2 is a detailed section of the area circled as “A” in FIG. 1, and

FIG. 3 is a section of one embodiment of a TRF closure system inaccordance with the present invention which shows the multiple layers ofmaterial that make up the system.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a traditional TRF closure system of the known art.

The traditional TRF system comprises a ring 1, a plug 5, and a foil 9.

The ring 1 of the traditional TRF system comprises a seaming curl 2, avertical sealing surface 3 that defines an orifice to allow access to acontainer, and an inwardly facing cut edge 4 of a foil.

The plug 5 of the traditional TRF system comprises a panel 6, asubstantially vertical sealing surface 7, and an outwardly extendingflange 8 allowing the plug to be levered from the orifice in the ring.

The foil 9 of the traditional TRF system extends across the inside ofthe TRF system to the sealing material 10 around the periphery in theseaming curl 2. Alternately, the foil 9 can be heat sealed to a flatsection of the ring, not shown. The foil 9 provides the primary seal forextended shelf life prior to opening.

The traditional TRF closure system has 3 critical dimensions, namely anominal diameter D measured as shown, a ring diameter d_(R), and a plugdiameter d_(p). The interference seal between the ring 1 and the plug 5is provided by selecting d_(p) to be sufficiently larger than d_(R) sothat a seal and grip is achieved, but not so large that insertion of theplug is excessively difficult. The range of acceptable interference isknown to those skilled in the art and is embodied in manufacturingspecifications for such parts.

FIG. 2 shows in greater detail the critical seal areas of thetraditional TRF system.

FIG. 3 shows one embodiment of the composite foil 17 of the presentinvention. The composite foil comprises successive layers of paper layer1, a polymer layer 2, an aluminium foil layer 3, and another polymerlayer 4.

The paper may be any suitable paper. Suitable paper includes a 35 gsm or50 grams per square metre (gsm) bleached kraft sheet made by AustraliaPaper. Alternative options include grammages ranging from 25 to 100 gsm.The functions of the paper layer 1 are: (a) bulk at low cost, (b) hightensile strength to permit seaming without fracture, (c) easy tearingfor consumer access, and (d) minimise risk of a consumer being cut byexposed edges of a ruptured composite foil.

The polymer layer 2 comprises a co-extruded copolymer of (a) a lowdensity polyethylene (LDPE) in the section of the layer 2 that joins thepaper layer 1 and (b) an ethylene acrylate acid resin adjacent thealuminium foil. The LDPE layer is about ⅔ of the total of thickness ofthe layer 2. The thickness of the layer 2 ranges from 8 to 30 um, and ispreferably 12 um. The polymer layer 2 is provided to adhere together thepaper layer 1 and the aluminium foil layer 3. The LDPE is selected onthe basis of its capacity to adhere to paper and the ethylene acrylateacid resin is selected on the basis of its capacity to adhere toaluminium.

The aluminium foil layer 3 in the composite foil is 30 um in thickness,but could conceivably range from 15 to 60 um in thickness. The functionof the aluminium foil is to provide high oxygen and moisture barrierproperties, both of which are important for long term shelf stability ofan unopened container. The aluminium foil layer 3 also contributes tothe mechanical properties of the composite foil.

The bottom layer 4 is a co-extruded co-polymer. The bottom layercomprises (a) a LDPE filled with 30% talc to weaken the overallstructure, with this material forming an exposed surface of thecomposite foil and (b) a terpolymer of ethylene methyl or butyl acrylategrafted with a maleic anhydride to adhere the layer 4 to the aluminiumfoil layer 3. Preferably the thickness of this layer is 20 um, but canconceivably range from 15 to 50 urn. An important function of the bottomlayer 4 is to protect the aluminium of the foil layer 3 from oxidationand other undesirable chemical reactions and to provide a layer of amaterial that is approved for direct food contact.

Many modifications may be made to this invention shown without departingfrom the spirit and scope of the invention.

That which is claimed:
 1. A foil of a tagger ring foil (TRF) closuresystem for a container comprising a composite of two or more layers madefrom different materials, wherein at least one layer comprisesaluminium, and having a board burst strength, when measured withAustralian Standard (AS) 1301.438s, of less than 400 KPa and a crossdirection ring crush resistance pressure, defined as the ring crushmeasured using AS 1301.407s, divided by 0.152 and multiplied by the foilthickness measured using AS 1301.426s, of less than 10 MPa so that, inuse, when the foil is part of a TRF closure system on a container andthe foil is ruptured to gain access to the contents of the container,the ruptured foil does not form a sharp edge.
 2. The foil defined inclaim 1 wherein the materials that form the layers of the composite foiland the combination of the layers are selected so that the foil can beprocessed in a conventional container manufacturing process thatincludes forming the container with a TRF closure system.
 3. The foildefined in claim 1 comprising a composite of the following layers:paper, a first polymer, an aluminium layer comprising one of analuminium and an aluminium alloy, and a second polymer.
 4. The foildefined in claim 3 wherein the paper ranges in thickness between 25 and100 gsm.
 5. The foil defined in claim 3 wherein the first polymer layerranges in thickness of between 10 and 30 μm.
 6. The foil defined inclaim 3 wherein the polymer of the first polymer layer comprises a lowdensity polyethylene co-extruded with an acrylic acid.
 7. The foildefined in claim 3 wherein the aluminium layer has a thickness ofbetween 7 and 60 μm.
 8. The foil defined in claim 1 further comprising afiller for reducing the board burst strength or the ring crushresistance pressure to a required level.
 9. A tagger ring foil (TRF)closure system for a container that comprises the composite foil definedin claim
 1. 10. A container that comprises the tagger ring foil (TRF)closure system defined in claim
 9. 11. The container defined in claim 10wherein the composite foil of the closure system comprises a paper sideand is applied to the container so that the paper side of the foil is anoutward facing side of the foil.
 12. The container defined in claim 10wherein the container is a metal container.